Method of constructing radome



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METHOD OF CONSTRUCTING RADOME Filed Sept. 15, 1965 2 Sheets-Sheet 1INVENTOR. DONALD L. LOYET y 14, 1968 D. L. LOYET 3,381.3;444

METHOD OF CONSTRUCTING RADOME Filed Sept. 15, 1965 2 Sheets-Sheet 2 Fig..9

INVENTOR. DONALD L. LOYET Fig. 7 BY CCCMZEWAGENT r0 NEY United StatesPatent Gfice 3,383,444 METHOD OF CONSTRUC'HNG RADOME Donald L. Loyet,Palos V'erdes Peninsula, Califl, assignor, by mesne assignments, to theUnited States of America as represented by the Secretary of the NavyFiled Sept. '15, 1965, Ser. No. 487,642

r 2 Claims. (Cl. 264-87) ABSTRACT OF THE DISCLOSURE A high-strengthlow-weight radome of high radar transparency and method of making same,which method includes filling a radome-shaped mold with slip material,applying pressure to the mold contents, and then removing excess slipmaterial to leave a thin-wall hollow core in the form of a radome. Byrepeating the process with slip material of different electricalcharacteristics, the microwave attenuation characteristics of the radomemay be varied.

This invention relates to the method of constructing dielectric wallsfor the transmission of microwave or centimetric electromagneticradiation. It is particularly directed to radomes for guided missilesand the like.

The many interrelated factors which make up a satisfactory radomeconstruction require a balanced design which is adapted to theenvironment and the type of signal to be transmitted. Thus an airborneradome must be strong, light, vibration resistant, corrosion resistant,smoothly contoured, resistant to thermal shock, resistant to rain,weathertight and must be fabricated by a process which is simple, doesnot require grinding or other ma-- chining operations and permits greatreproducibility time after time within acceptable dimensional limits. Ofcourse in addition it must permit maximum transmission of radiated wavestherethrough with minimum distortion and degradation. 1

Heretofore many diiferent types and shapes of micro= wave transparentwall constructions have been proposed. When used on missiles these maybe provided various shapes such as ogival, conical, the Von Kar-man andNewtonian, all of which have their advantages.

When a radome is formed of ceramic material it has been customary in thepast to use a thin-wall radome or a one-half wavelength thick radome asthe basis of the ra dome design. However, recently much effort has beengiven to the construction of ceramic sandwich radomes which transmitelectromagnetic radiation of greater electrical bandwidth and are ofless weight. Furthermore, diamond grinding of radome surfaces isavoided.

Of course, airborne radomes must not only protect the contents of themissile head, but must be weatherproof and of sufiicient strength toresist missile vibration and bending moments, the latter being greatestat the joint where the radome is secured to the missile body. In someconstructions a middle layer of a foam or a honeycomb of plasticmaterial is located betwen two outer walls of thin skins of higherdielectric constant, however this meth= d of gaining physical strengthusually results in loss of desired electrical characteristics.

Accordingly it is one object of the present invention to provide amethod of constructing a radome which alfords a minimum interference tothe transmittal of high frequency signals but has sufiicient strength toresist normal vibrations, bending moments and the impact of rain.

A further object is to provide a method of constructing radomes which issimple, quick, inexpensive and practical and wherein successive partsmade thereby are uniform in dimension and in microwave transmissioncharacteris= tics.

3,383,444 Patented May 14, 1968 Additional objects and many of theattendant advantages of this invention will be readily apparent as thesame becomes better understood by the reference to the followingdetailed description when considered in conjunction with theaccompanying drawings wherein:

FIG. 1 is a vertical sectional view through a mold construction formanufacturing the device of the present invention;

FIG. 2 is a view similar to FIG. 1 showing the step of applying fluidpressure to the mold contents;

FIG. 3 shows the mold tilted to permit excess slip to be pouredtherefrom leaving a thin coating on the mold faces;

FIG. 4 discloses an additional step wherein a small amount of slip isreinserted into the mold to form a solid radome tip;

FIG. 5 is a vertical section through a radome constructed in accordancewith .the process illustrated in FIGS. 1-4;

FIG. 6 is a view similar to FIG. 5 showing a sealing ring closing thespace between radome shell walls;

FIG. 7 isan enlarged vertical cross-sectional view taken on a linesubstantially corresponding to line 7-7 of FIG. 6;

FIG. 8 is a view similar to FIG. 7 showing one means for securing aradome in place; and

FIG. 9 is a view showing an alternate form of radome wherein severallayers of material are built up.

Referring now to the drawings wherein like reference charactersdesignate like or corresponding parts throughout the several views,there are illustrated in FIGS. 1 through 4 the steps employed to form aradome embodying the characteristics of the present invention.Throughout this description the steps will be discussed as performed tomold a double thin-wall'radome of the general shape illustrated in FIG.5. It will be apparent however, that the ultimate radome shape dependsupon many design considerations and that other shapes within the spiritof the present invention may readily be molded bythis method. I

As shown in FIG. 1 there is provided a lower mold half 10 and an uppermold half 11 which may be formed from any suitable absorbent materialsuch as plaster of Paris. These mold members when fitted togetherprovide a space therebetween of the desired shape and characteristics.In making the molds, due allowance is made for shrink so that moldedparts are properly dimensioned upon completion aril no further grindingor machining is required.

As shown, there may be provided an inlet 12 at the upper left handcorner of the mold through which a suitable liquid called slip may beintroduced intojt he mold interior. This slip may be in the form of avehicle having finely dispersed ceramic particles throughout. The moldis filled until liquid slip emerges from the mold through port 13.

A portion of the liquid vehicle of the slip thereof is absorbed into theplaster of paris leaving the finely dispersed ceramic material in alayer along both surfaces of the mold.

The next step is shown in FIG. 2 where the exit 13 is shown obstructedby a plug 14 and at this step pressure is applied to the mold contentspreferably through inlet 12. After the parts have been permitted to setso as to allow a build up of the desired wall thickness on bothmoldsurfaces the pressure is released, exit 13 is unblocked and When the tiphas set the upper mold half 11 can be removed so that the cast radomemay be lifted out of the lower mold half. The result is a radome of thecharacter illustrated in FIG. wherein an inner wall 15 and a Spacedouter wall 16 are interconnected at their tips by a slug 17 ofsolidified casting material. This slip serves not only to providestrength at the critical tip area of the radome but also, being of thesame homogeneous material as the inner and outer walls 15 and 16,provides minimum interference with the high frequency radiations beingtransmitted therethrough.

The composition of the slip or slurry may vary from radome to radome andalso from one sandwich layer to another. Examples of suitable slipmaterial are ceramic based materials, plastic and alumina. When desiredsmall beads of plastic or microspheres may be added to the slipmaterial. This addition has been found to improve resistance to theeffect of rain drops on the radome.

In order to complete the radome an annular spacer of ceramic material 18may be placed between the open ends of walls 15 and 16 of the radome.This spacer ring may be cemented in place by a portion of the slipmaterial from which the radome is made and materially strengthens thiscritical area. In FIG. 7 there is provided a greatly enlarged view ofthe after portion 20 of a radome with the collar in place and in FIG. 8there is shown the manner in which the rear edge 21 of the radome may bereceived in a ledge 22 formed in the mating forward end 24 of themissile body.

In the foregoing there has been described the manner of manufacturing adouble thin-wall radome having a homogeneous tip portion for addedstrength. It will readily be apparent however that the present processcan also be applied to other forms of radome construction. For example,to produce a sandwich type wall the initial step may be repeated twice,each time with different material and perhaps a different upper moldhalf 11 and, if desired, the remaining central space may be filled withother material. By this means a sandwich type radome wall correspondingto that illustrated in FIG. 9 is provided. There the two outer thin-wallhalfwave sections A are reinforced by inwardly located additional thinwalls B and a central core C of suitable material will complete thesandwich layers.

Numerous variations of this technique may be employed whereby a ceramicradome with a homogeneous tip may be constructed and, by variations inthe material being used, desired electrical characteristics may beselected. If desired, suitable apertures, not shown, may be provided inthe wall of the radome to equalize pressures between the inside andoutside surfaces. It will be apparent that a radome produced by theabove described process has a number of desirable characteristics. It isrelatively light in weight, has low interference with electricaltransmission therethrough, has a reinforced nose portion for strengthagainst rain and ice, has a reinforced missile contacting skirt whichprovides maximum resistance to bending moment, and yet allowsdifferential expansion at this point of contact with the missile.Furthermore the radome is made of materials which are readily availableand can readily be fabricated in the manner described to provide goodreproducibility item after item, thus uniformity of product is assured.It is furthermore low in cost and the resulting radome does not requiremachining, grinding or other working prior to use.

As is understood in the art, strength may be provided by a solid radomewall and a sandwich type construction thereof has greater resistance tothermoshock. However, the double thin walls illustrated provide the besttransmission of electrical characteristics, and, when formed ofhomogeneous material and strengthened in the manner described provide anexcellent radome for hypersonic missiles. This is particularly true whenfrequencies above the X-band and approaching the K-band are involved.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described,

1 claim.

1. The method of forming a strong, light-weight radome with lowattenuation effects on microwave energy passed therethrough comprising;

(a) filling upper and lower mold portions which define a desired radomeshape with a castable slip mate rial;

(b) applying pressure to the contents of said mold;

( c) removing excess slip material to leave a thin Wall adjacent eachmold surface; and

(d) repeating steps (a), (b) and (c) with slip material of differentelectrical characteristics to form additional thin walls of differingelectrical characteristics.

2. The method of claim 1 including the final step of applying a centralcore of such slip material to form a sandwich type radome.

References Cited UNITED STATES PATENTS 1,693,429 11/1928 Austin 26487 X1,733,729 10/1929 Gouverneur et a1, ....H 264-86 3,195,138 7/1965 Beck343 -872 3,292,544 12/1966 Caldwell et a].

OTHER REFERENCES Ceramic Age, Fused Silica for Missile Components,August 1960, vol. 76, No. 2, pp. 3238.

Ceramic Age. Fused Silica for Missile Components, September 1960. vol.76, No. 3, pp. 23-28.

ROBERT F. WHITE, Primary Exatmflterv 'i. H. SILBAUGH, AssistantExaminer.

